“Since 1926, the average annual return for US stocks has been a little more than 10%, and this seems to be pretty common knowledge for even neophyte investors,” Vanguard analyst Donald Bennyhoff wrote. “So 10% would seem to be a reasonable expectation for an average year, right? Our illustration … shows how often that assumption is erroneous, but it is also irrelevant.”

Again, just get it out of your head that a year may turn out to be an average year.